Turbocharging: Key Technology for High-Performance Engines

Engine technology Turbocharging: Key technology for high-performance engines

Authors: The performance of an internal combustion engine can be increased by adding turbocharging. A turbocharger compresses the air so that more oxygen flows into the Dr. Johannes Kech combustion chamber. In this way, more fuel is burned and the power output of the Head of Development Turbocharging engine increases accordingly. The turbocharger is driven by exhaust gas, which makes turbocharged diesel engines very efficient. MTU develops this key technology for Ronald Hegner high-performance engines in-house. Team Leader, Design of Turbocharging Systems Turbocharger development and production at MTU engine power ratings from 400 to 10,000 kW. Tobias Männle Turbocharging is an integral component of the Turbochargers are purchased for engine designs Team Leader, Fluid Dynamics and Thermal engine design concept. It shapes the character- in which synergy effects with the commercial Analyses istics of the engine more than almost any other vehicles sector can be used. system, as it affects its economy, dynamics and emission characteristics. This is why turbocharg- The global market for turbochargers is dominat- ing is one of MTU’s key technologies. MTU has a ed by car and commercial vehicle applications. tradition of maintaining the expertise for devel- By comparison, the number of turbochargers oping and producing its turbochargers in-house. fitted to industrial engines is negligible. The re- The range of MTU turbochargers extends across sult is that turbocharger manufacturers rarely

www.mtu-online.com produce specialized designs for industrial engine manufactures. Where customers’ requirements Fig. 1: Current MTU turbocharger program (ZRT 12, 13, 35, 36, 57) MTU’s current turbocharger family includes five series and is based on a concept of using as many of the engines are such that they cannot be sat- common parts as possible. isfied by purchased turbochargers, MTU develops and produces the turbochargers itself. A exhaust inlet Taking all engine series into account, MTU pro- B exhaust outlet duces roughly 50 percent of the turbochargers C charge air inlet in-house. The present range of MTU turbo D charge air outlet chargers encompasses five series — the ZRT 12, cooling water ZRT 13, ZRT 35, ZRT 36 and ZRT 57 (see Figure 1), and is based on a concept of using as many common parts as possible. In the case of the new Series 4000 engine for rail applications with regulated two-stage turbocharging, for instance, all three turbochargers in the system are identi- cal. This simplifies the logistics in production and the supply of spare parts to customers.

Due to its in-house development and production of turbochargers, MTU is in a position to meet customer demands for highly responsive and pow- erful engines. MTU matches the turbocharging system to the engine so that it delivers reliable 1 turbine wheel high performance across the entire range of en- 2 compressor wheel gine specifications, from sea level to an altitude of 3 pressure ratio p /p 4,000 meters, and from low to extremely high 2t 1t reduced volumetric flow V ambient temperatures. As the MTU turbochargers 4 red. are configured specifically to meet the engine specifications, they are easily integrated into the small size series ZRT 12, ZRT 13 medium size series ZRT 35, ZRT 36 large size series ZRT 57 overall engine package. This makes the engines 1 Ø 103-123 mm 1 Ø 158-185 mm 1 Ø 245 mm very compact — a decisive advantage in applica- 2 Ø 115-135 mm 2 Ø 179-210 mm 2 Ø 265-270 mm tions where installation space is at a premium. 3 up to 5.2 3 up to 5.4 3 up to 5.4 4 0.2-0.9 m3/s 4 0.8-2.0 m3/s 4 1.8-3.5 m3/s In recent years, the operating conditions of some applications have become tougher. The power cles, which also has an effect on the service life es into account in the development of its turbo- units are subjected to a high number of load cy- of the turbochargers. MTU has taken these chang- chargers, has further optimized the time between overhauls (TBO) and brought this in line with the Fig. 2: Use of three-dimensional computation procedures for simulating the airflow and the mecha- engines. In the case of the Series 4000 rail en- nical structural loads to optimize turbocharger performance gine, for example, turbocharger TBO is as high as The turbochargers must retain the required characteristics throughout their entire service lives. To this 15,000 hours depending on the number of load end, MTU works with three-dimensional computation procedures to simulate the airflow and the mechanical structural loads. cycles per hour. This means short maintenance periods and costs — this also applies to the turbochargers. In the turbocharger development processes, MTU makes use of the possibilities offered by efficient calculation and simulation tools.

When a new turbocharger is produced, it has already gone through a whole sequence of analy- tical optimization processes in thermodynamics, structural mechanics, durability and containment strength, for example, by the time it is put on the test bench. Analysis fundamentally involves opti mization of the component by the use of three- dimensional computation procedures for simulating the airflow and the mechanical structural loads (see Figure 2). In this way, MTU ensures that the turbochargers have the required characteristics when they finally go into service and retain them throughout their entire service lives.

Turbochargers are subjected to high thermal

Turbocharging: Key technology for high-performance engines | MTU | 2 With variable turbine geometry, the power delivery and response characteristics of the turbocharger can be better adapted to the dynamic engine operating conditions. The exhaust passes over adjustable guides to the turbine blades so that the turbine spools up quickly at low engine speeds and subsequently allows high exhaust gas flow rates.

Turbocharger with variable turbine geometry (VTG) loads in operation. Accordingly, seals and bear- turbochargers. Within a design series, the speeds as possible. ings are thermally isolated and, if necessary, turbocharging is matched to the specific For applications that demand even more dynamic water-cooled. To limit the surface temperature, equirements of the particular application. power response, particularly in marine applica- MTU uses a water-cooled impeller blade on This means that a power generation engine, tions, MTU uses the sequential turbocharging highly turbocharged engines, which simultane- which always runs at the same speed, needs principle. It involves multiple turbochargers be- ously relieves some of the load on the inter- a different turbocharger setup than a vehicle ing sequentially linked. One turbocharger pro- cooler. In marine applications, the turbine is engine. A vehicle engine is driven dynamically duces the boost pressure for low engines speeds, cradled in a water-cooled connecting block — it has to deliver high performance from idling and when the engine is revving faster or when (see Figure 3). The turbochargers thus also speed right through to maximum revs — and more power needs to be developed, additional satisfy the SOLAS Directive (Safety of Life at the turbocharger characteristics have to be turbochargers are added so that sufficient air Sea) for marine applications, which stipulates matched to the broad power band. The chal- is delivered to the cylinders. that, for safety reasons, the surface tempera- lenge is that a turbocharger can be set up ture may not exceed 220 degrees Celsius. either for a wide speed range or a high boost To provide highly responsive engine dynamics, pressure. For engines earmarked for dynamic the Series 890 engines, which are designed for Implementation of turbocharging at MTU applications, therefore, MTU has designed the high performance in military vehicles, have vari- As a matter of principle, MTU equips all en- turbochargers to deliver sufficient boost pres- able turbine geometry. With this technology, the gines from the various engines series with sure while covering as broad a range of engine exhaust passes over adjustable wings to the turbine blades so that the turbine spools up quickly at low engine speeds and subsequently allows high exhaust gas flow rates. For the new engine generations to achieve high performance, MTU uses two-stage turbocharging. In the early 1980s, MTU already equipped the Series 1163 with com- pletely integrated two-stage turbocharging with intercooling. Up to five sequentially arranged turbocharger groups consisting of high and low- pressure stages enable the engine to deliver 7,400 kW of power.

New demands on turbocharging due to new emissions legislation Today, the ongoing development of engines is definitively determined by the continual tightening of emissions standards. This means that additional systems that prevent the production of diesel particulates or nitrogen oxides during the combustion process or clean them further downstream such as the Miller process, exhaust gas recirculation (EGR), selective catalytic reduc- tion (SCR) or a diesel particulate filter (DPF) have to be integrated into the overall engine design concept. For MTU, turbocharging is one of the key technologies in these low-emission con- Fig. 3: High-performance turbocharger with water-cooled casing and compressor impeller Using water cooling for the casing and compressor impeller ensures that the engine’s surface tempe- cepts. This is because it is only with a compat- rature is limited, which makes MTU turbochargers thermally very durable. ible turbocharging system that the tendency of these additional systems to negatively affect

Turbocharging: Key technology for high-performance engines | MTU | 3 engine performance and responsiveness can be followed by further compression in high-pres- coolers. The first is located between the low- prevented. A common feature of all emissions- sure turbochargers. Control of the turbocharg- pressure and the high-pressure stage, and the reducing technologies is that they diminish er system is integrated into MTU’s electronic second downstream of the high-pressure stage. the effect of the turbocharging. The Miller pro- engine management system ECU ( Engine Con- Intercooling provides more efficient compression cess, exhaust gas recirculation and diesel par- trol Unit), which was developed in-house. in the following high-pressure stage, which leads ticulate filter create higher exhaust to a higher efficiency level of the turbocharging backpressure; exhaust gas recirculation increas- The innovative regulated two-stage turbocharging system. In the case of all MTU engines, the inter- es the air mass that has to be delivered to the system is being used for the first time for the new coolers are highly integrated into the engine unit cylinder. To put it simply, the turbocharger has Series 4000 engine for rail applications. It meets and have a very small space requirement. to compress the air at a higher rate, i.e. it must EU Directive 97/68/EC Stage IIIB emission re- force more air into the combustion chamber to quirements that have been in place for diesel Summary provide the same amount of oxygen for combus- locomotives in Europe since 2012. In the current Turbocharging helps MTU engines to achieve tion as before. engine series for other mobile applications such low fuel consumption and high performance as construction and industry, regulated two-stage across a broad range of operating speeds. In As research by MTU has shown, the single- turbocharging is implemented respectively addition to MTU’s other key technologies, it is stage turbocharging previously used will no definitely planned. For stationary applications a major component of the strategies to comply longer be sufficient for most applications in such as power generation, in which the de- with the increasingly tougher emission restric- the future. For engines designed to comply mands on turbocharger dynamic response are not tions to come without sacrificing engine per- with tough emissions standards, the specialist so high, the more economical single-stage turbo- formance or efficiency. The company has a for propulsion solutions will opt for regulated charging will continue to be used. tradition of developing and producing its own two-stage turbocharging (Figure 4). This is a turbochargers for high-performance applica- system that ensures a constantly high rate of Intercooling tions in-house. They are configured specifically intake air delivery to the engine at all operat- When the air is compressed by the turbocharger, to satisfy the high demands of the engines ing points and even under extreme ambient it heats up. Intercooling further increases the air in terms of economy, performance, dynamic res- conditions (intake air temperature, altitude, density so that greater air mass and thus more ponse and service life. Because of the high backpressure). It involves pre-compression of oxygen enters the cylinder. The regulated two- level of integration of the MTU turbochargers the intake air by low-pressure turbochargers stage turbocharging system works with two inter- in the engine package, customers benefit

Fig. 4: Regulated two-stage turbocharging to meet current and future emission standards Since single-stage turbocharging will no longer be sufficient to comply with the increasingly tougher current and future emission standards, MTU opts for a regulated two- stage turbocharging in most current engine series.

1 charge air cooler 2 intercooler

3 low-pressure compressor 4 low-pressure turbine

5 high-pressure turbine 6 high-pressure compressor

A from high-pressure compressor to charge air cooler B from charge air cooler to cylinder bank C intake air D exhaust outlet E from intercooler to high-pressure compressor

Turbocharging: Key technology for high-performance engines | MTU | 4 Glossary

Single-stage turbocharging In the case of single-stage turbocharging, the boost pressure for the entire range of engine speeds and loads is generated by a single turbocharger.

Sequential single-stage turbocharging In the case of sequential single-stage turbo charging, individual turbochargers are added sequentially in parallel depending on the engine speed and load by means of valves in the intake and exhaust systems.

Turbocharging: Key technology for high-performance engines | MTU | 5 Glossary

Sequential two-stage turbocharging Basically speaking, sequential two-stage turbocharging operates in the same way as sequential single-stage turbocharging. However, instead of an individual turbocharger in each case, a pair of turbochargers is added or disconnected as required.

Regulated two-stage turbocharging Photo credits: Page 1 to 8, Adam Wist for MTU Friedrichshafen GmbH. 1 to 8, Adam Wist for MTU Friedrichshafen GmbH. Photo credits: Page In the case of regulated two-stage turbocharging, two turbochargers are connected in series. In the system configuration employed by MTU, the exhaust flow from the cylinders is split so that part of it passes through the high-pressure (HP) turbine and the rest is diverted through a bypass by a controllable wastegate valve. The entire mass flow then flows through the low-pressure turbine (LP).

MTU Friedrichshafen GmbH A Rolls-Royce Power Systems Company www.mtu-online.com January 2014

MTU is a brand of Rolls-Royce Power Systems AG. MTU high-speed engines and propulsion systems provide power for marine, rail, power generation, oil and gas, agriculture, mining, construction and industrial, and defense applications. The portfolio is comprised of diesel engines with up to 10,000 kilowatts (kW) power output, gas engines up to 2,150 kW and gas turbines up to 35,320 kW. MTU also offers customized electronic monitoring and control systems for its engines and propulsion systems.

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